Christine Lagarde consolidated her status as front-runner for the top job at the International Monetary Fund on Friday as several African leaders declared their support for the French finance minister, and a potential rival declined to challenge her.

Lagarde's visit to the annual meeting of the African Development Bank in the Portuguese capital proved to be a venture into friendly territory. One African finance minister after another backed Lagarde to be the next IMF managing director on the day that nominations closed.

The Moroccan finance minister, Mezouar Salaheddine, set the tone for the day when he said Lagarde had Morocco's unqualified support. "I know her qualities, her commitment to the developing world and her capabilities," Salaheddine said. "She is sincere and reassuring on the importance of Africa and capable of bringing a new dimension to the IMF. It is clear that she is the best candidate."

The prospects of an African candidate evaporated after South Africa's former finance minister, Trevor Manuel, ruled himself out. Announcing his decision, Manuel criticised the long tradition of appointing a European at the head of the IMF. "I think a lot more could be done, a lot more should have been done to persuade Europeans that this birthright is not a birthright," Manuel said.

The only declared rival to Lagarde as the deadline for nominations expired was the head of the Mexican Central Bank, Agustín Carstens, after Kazakhstan's central bank governor, Grigori Marchenko, withdrew at the 11th hour. Carstens has not won wide support from other emerging economies.

On Thursday the African Union said it was time for an African to be IMF managing director, arguing that this would give the continent's members a louder voice. But the strong backing Lagarde enjoyed from African finance ministers showed the lack of an African consensus.

Lagarde gave a characteristically polished performance in Lisbon, speaking in French and flawless English at a VIP lunch and handling questions in both languages at a press conference where the finance ministers of Ivory Coast, Charles Koffi Diby, and the Democratic Republic of the Congo, Matata Ponyo, backed Lagarde.

"I am not the candidate of Europe, I am not the candidate of France, I am the candidate to serve the 187 [members] of the IMF, so that the institution can deliver the services they need," said Lagarde, who has been to India and China as part of her lobbying blitz. Her next stop is Saudi Arabia.

Lagarde made a point of showing that she would not adopt a doctrinaire approach at the IMF, stressing her respect for the organisation's diversity. She said the IMF should not adopt a "one size fits all" approach, but adjust to different circumstances and show understanding for countries that needed support.

"The IMF is not the doctrinal property of such and such a school," she said, a reference to criticism of the institution's default position of forcing ailing economies to adopt austerity measures.

Lagarde even showed her sense of humour. When asked whether she would appoint an African number two in view of the strong support shown for her in Lisbon, she said with a smile: "I'm looking at No 1 at the moment."

The one cloud over her prospects is a legal investigation into her role in a 2008 arbitration. A top French court yesterday put off until 8 July its decision on whether to open a formal inquiry into allegations that she abused her authority in approving a €285m (£252m) payout to a businessman friend of President Nicolas Sarkozy.

"I'm not at all concerned by any inquiry," she said. "There is absolutely no ground for it. I am extremely relaxed and confident about it."